Chemistry - Complete d-block Question with Solution | TestHub

The atomic number $Z=25$ corresponds to Manganese (Mn).

The electronic configuration of neutral Mn is $[Ar]3d^{5}4s^2$.

For the divalent cation Mn${}^{2+}$, two electrons are removed from the outermost $4s$ orbital.

The electronic configuration of Mn${}^{2+}$ becomes $[Ar]3d^5$.

According to Hund's rule, the five electrons in the $3d$ subshell will singly occupy the five $d$-orbitals.

Therefore, the number of unpaired electrons is $5$.

Answer: $5$